Article date: May 2000
By: Minna Vainio, Bertil B Fredholm, Kid Törnquist in Volume 130, Issue 2, pages 471-477
The effect of thyrotropin (TSH), on adenosine A1 receptor expression in thyroid FRTL‐5 cells was examined by [3H]‐1,3‐dipropyl‐,8‐cyclopentyl xanthine ([3H]‐DPCPX) binding on cells in suspension and on membrane preparation, and by in situ mRNA labelling.
The estimated KD for intact cells was 0.19 nM and about 47,000 binding sites per cell were found in cells constantly grown in the presence of TSH.
Three days deprivation of TSH decreased the number of [3H]‐DPCPX binding sites without any significant effect of KD. Reintroduction of TSH to the cells returned the higher level of A1 receptors both in suspension binding studies on whole cells and on membrane preparations.
In situ hybridization revealed that TSH evoked an increase in the number of cells densely labelled with a probe against A1 receptor mRNA.
The potency of the A1 receptor agonist N6‐cyclohexyladenosine (CHA) as an inhibitor of cyclic AMP formation induced by forskolin was increased in TSH‐treated cells, with a shift in the IC50 from 2.05 nM in TSH‐deprived cells to 0.14 nM in TSH‐treated cells.
Since the activation of A1 receptors inhibits TSH‐mediated cyclic AMP signalling, our results suggest a regulatory feedback mechanism between signalling via adenosine A1 receptors and TSH receptors.
The effect of thyrotropin (TSH), on adenosine A1 receptor expression in thyroid FRTL‐5 cells was examined by [3H]‐1,3‐dipropyl‐,8‐cyclopentyl xanthine ([3H]‐DPCPX) binding on cells in suspension and on membrane preparation, and by in situ mRNA labelling.
The estimated KD for intact cells was 0.19 nM and about 47,000 binding sites per cell were found in cells constantly grown in the presence of TSH.
Three days deprivation of TSH decreased the number of [3H]‐DPCPX binding sites without any significant effect of KD. Reintroduction of TSH to the cells returned the higher level of A1 receptors both in suspension binding studies on whole cells and on membrane preparations.
In situ hybridization revealed that TSH evoked an increase in the number of cells densely labelled with a probe against A1 receptor mRNA.
The potency of the A1 receptor agonist N6‐cyclohexyladenosine (CHA) as an inhibitor of cyclic AMP formation induced by forskolin was increased in TSH‐treated cells, with a shift in the IC50 from 2.05 nM in TSH‐deprived cells to 0.14 nM in TSH‐treated cells.
Since the activation of A1 receptors inhibits TSH‐mediated cyclic AMP signalling, our results suggest a regulatory feedback mechanism between signalling via adenosine A1 receptors and TSH receptors.
British Journal of Pharmacology (2000) 130, 471–477; doi:10.1038/sj.bjp.0703325
DOI: 10.1038/sj.bjp.0703325
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